Electrical heating apparatus



Sept- 1946. w. M. ROBERDS 2,408,229

' ELECTRICAL HEATING APPARATUS Filed April 50, 1943 Patented Sept. 24-,1946 ELECTRICAL HEATING APPARATUS Wesley M. Roberds, Collingswood, N.J., assignor to Radio Corporation of America, a corporation of DelawareApplication April 30, 1943, Serial No. 485,133

12 Claims. 1

This invention relates to electrical heating apparatus, and moreparticularly to an induction heating applicator coil useful in inductionheating apparatus.

The use of high frequency electrical energy for case hardening ferrousmetals is now fairly well known. In general, the work to be hardened isscanned by an inductor coupling coil which is connected to a source ofradio frequency energy, the coil heating the work fairly instantaneouslyby induction. The form of coupling coil most generally employed is asubstantially single turn, helical winding with its ends overlapped inslightly spaced relation longitudinally of the coil in order to embracethe entire circumference of the work. While such a coil usually providessatisfactory results where the entire surface of the work is to behardened, it is not satisfactory in all cases for the reason that itdoes not heat the work instantaneously along a circular portion thereof,but along a helical portion. Thus, when the work is scanned at certainrates, some parts thereof become heated twice due to the overlapped endsof the coil.

Asi e from the foregoing, there are some cases in which it is desirableto harden only a portion of the work, as, for example, the base or someother small circumferential area of a cylindrical member. In such cases,the helical coupling coil is not at all satisfactory for the reason thatit forms a helically shaped, hardened layer, instead of a circularlyshaped layer.

The primary object of my present invention is to provide an improvedinductor coupling coil which will be free from the aforementioneddisadvantages.

More particularly, it is an object of my present invention to provide animproved inductor coupling coil which will produce, for practicalpurposes, uniform heating along a circle which lies in a given planethrough the work.

Another object of my present invention is to provide an improvedinductor coupling coil as aforesaid which will produce practicallyuniform heating of the work opposite the point where the current entersand leaves the coil, as Well as at other points on the work embraced bythe coil.

Still another object of my present invention is to provide an improvedinductor coupling coil as aforesaid which is simple in construction, caneasily be fabricated, is economical in cost, and is highly efilcient inuse.

In accordance with my present invention, I provide an inductor coilwhich is formed of a single turn, annular conductor having substantiallyuniform overall thickness throughout its entire circumference, asdistinct from the helical form of coupling coil which, at its overlappedends, has a thickness in excess of twice the thickness of the conductorof which it is made. My improved coupling coil is formed with acircumferential slot extending clear through from the outer to the innerperimeter thereof and with which communicate two longitudinallyextending slots each extending from an opposite end of the coil. In thisway, there are formed on my improved coupling coil two overlappingterminal portions separated from each other by the gap provided by theaforementioned circumferential slot.

Preferably, although not necessarily, the annular conductor of which myimproved coupling coil is made has a substantially triangular crosssection, its minimum thickness being either on the outside perimeter oron the inside perimeter of the coil depending upon whether the coil isto surround the work or whether it is itself to be surrounded by thework. The coupling coil is mounted upon a suitable support which maycomprise a tubular coil formed similarly to the prior art helical coils,and the aforementioned longitudinal slots are so formed in my improvedcoupling coil that they will converge toward each other from the outsideperimeter to the inner perimeter of the coil, whereby the current willbe led into and out of the coupling coil as nearly tangentially as isfeasible. Each of the overlapping terminal portions of my improved coilhas an overall thickness which is slightly less than half of the overallthickness of the conductor of the coil. Thus, the entire coil has asubstantially uniform thickness throughout its circumference.

The novel features" that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operation, aswell as additional objects and advantages thereof, will best beunderstood from the following description of one embodiment thereof,when read in connection with the accompanying drawing, in which Fig. 1is a plan view of one form of inductor coil according to my presentinvention, the coil being shown schematically connected to a highfrequency oscillation generator,

Fig. 2 is a sectional view taken on the line IIII of Fig. 1,

Fig. 3 is a view similar to Fig. 2 but with my improved coupling coilremoved in order to show 3 more clearly the supporting member therefor,and

Fig. 4 is a developed view of my improved coupling coil.

Referring more particularly to the drawing, wherein similar referencecharacters indicate corresponding parts throughout, there is shown anannular coupling coil l which consists preferably of a machined ring ofconductive material having a preferably triangular cross section, asclearly shown in Fig. 2. The ring I is formed substantially midwaybetween its ends with a circumferential slot 3 which extends radiallythrough the ring I from its outer perimter' Ia to its inner perimeter Iband preferably, although not necessarily, lies in a plane perpendicularto the axis of the coil I.

The ring I is also provided with a longitudinal slot 5 which extendsfrom. the upper end thereof downwardly to and communicates with the slot3, aswell as with a second longitudinal slot 'I WhiChis spacedcircumferentially from the slot 5 and'extends upwardly from the lowerend of the ring I to and also communicates with the slot '3. The ring Iis thus provided with a pair of overlapped terminal portions 9 and IIseparated in a direction parallel to the axis of the coil I by the slot3 which constitutes a gap therebetween. As will be noted most clearlyfrom Fig; 2, the terminal portion '9 ends at the slot 5, n

and the terminal portion II ends at the slot I. The slots 5' and 'I'converge toward each other as they approach the inner perimeter lb ofthe ring I '(see Fig. l) and may or may not extend through the ring I ina radial direction, as may be found most suitable. In any case, theoverall thickness of the coil or ring I throughout its entirecircumference, that is, at its outer perim eterla, is substantiallyuniform; the overall thickness of each terminal portion 9 and I I beingsomewhat less than half the overall thickness of the coil itself.

The ring member or coupling coil I is supported on a single turn,helically formed tubular member I3 to which it'may be secured in anysuitable manner in concentric relation therewith". Where, for example,the tubular support I3'is formed of metal, such as copper, the ringmember I, also preferably of cop-per, maybe soldered thereto, as, shownby the solder I5 in I igs. l and 2. A suitable cooling fluid, such ascold water, may be'fed through the tubular support I3 to cool thecoupling coil during operation and to prevent the solder from melting.Preferably, an insulating strip ll of mica or any other suitableinsulating material having a high dielectric strength is inserted in thegap lfibetween the overlapped ends of the tube I3 as well as in the gapprovided by the slot 3, which is in substantial alignment with the gap It, to prevent sparking between the terminal portions 9 and I I of theannular coil I. The end portions Ida of the supporting tube is may havesuitable input terminals 2|, preferably also of tubular construction,connected thereto. The coil I is coupled to a high frequency oscillationgenerator 23 through theterminals El and a coupling transformer 2-5 inwell known manner.

The form of my improved coupling coil shown in the drawing isparticularly adaptable for use with a cylindrical rod, shaft, or thelike, the surface of which is to be hardened along a thin, circular areaby placing the coil I around it and applying radio frequency powerthereto. Thus, the coupling coil I illustrated in the drawing isthickest at its outer perimeter and gradually tapers down to a minimumthickness at its inner perimeter lb. Of course, where the inner surfaceof a hollow, cylindrical member is to be hardened, as in the case of acylinder bore of an internal combustion engine, the ring I will be madethinnest at its outer perimeter and thickest at its inner perimeter, thecoupling coil I then being connected to the outer perimeter of thesupporting tube I3 instead of being nested within and connected to theinner perimeter thereof, as illustrated in Figs. 1 and 2. In any case,it should be apparent to those skilled in the art that, with my improvedcoupling coil, due to its uniform overall thicknessv throughout itsentire circumference,

uniform heating of the work along a circular path or area will result,and that the heating opposite the point where the current enters andleaves the coil will be the same as elsewhere around the coil.

Although I have shown and described but one embodiment of my invention,it will be apparent to those skilled in the art that many othervariations thereof, as well as changes in the one described, arepossible. For example, instead of mounting "1e coupling coil I on aconductive support, such as the tube I3, it may be mounted on anon-conductive support and the input leads 2| connected directly to theoverlapped terminal portions 9 and H.

and I may extend either in a radial direction across the coil 5 or insome other suitable direction, it being preferable, however, that theyshall converge toward each other as they approach the inner perimeterII) in such a manner relative to the bends Itb of the tube I3 that thecurrent Will be led into the coil I from one supporting tube end i3a andled out of the coil Ithrough the other supporting tube end 53a as nearlytangentially as possible, so as to avoid sharp or abrupt current pathchanges. Other variations will, no doubt, readily suggest themselves tothose skilled in the art. I therefore desire that my invention shall notbe limited except insofar as is made necessary by the prior art and bythe spirit of the appended claims.

I claim as my invention:

1. An inductor coupling coil for electrical heating apparatus comprisinga single turn, annular conductor having overlapped terminal portionsspaced from each other in a direction parallel to the axis of said turnto provide a gap therebetween, said turn having substantially uniformoverall thickness in said direction throughout the entire circumferencethereof.

2. An inductor coupling coil according to claim 1 characterized in thateach 'of'said terminal portions has an overall thickness in saiddirection which is less than half of the overall thickness of saidconductor in said direction.

3. An inductor coupling coil for electrical heating apparatus comprisinga single turn, annular conductor of substantially uniform overallthickness throughout its entire circumference in a direction parallel tothe axis thereof, said con: ductor having a circumferential slotextending radially therethrough and having also a pair ofcircumferentially separated longitudinal slots therein communicatingwith said circumferential s1ot,.one of said longitudinal slots extendingfrom one end of said turn toward said first named slot and the other ofsaid longitudinal slots extending from the other end of said turn towardsaid first named slot to thereby provide Also, the longitudinal slots apair of opposed, overlapping terminals spaced from each other by saidfirst named slot.

4. An inductor coupling coil according to claim 3 characterized in thatsaid longitudinal slots extend from the outer perimeter to the innerperimeter of said turn.

5. An inductor coupling coil according to claim 3 characterized in thatsaid longitudinal slots extend from the outer perimeter of said turn tothe inner perimeter thereof, and characterized further in that saidlongitudinal slots converge toward each other as they approach saidinner perimeter.

6. An inductor coupling coil according to claim 3 characterized in thatsaid longitudinal slots extend from the outer perimeter of said turn tothe inner perimeter thereof each in substantially a direction radiallyof said turn.

'7. An inductor coupling coil for electrical heating apparatuscomprising a single turn, annular conductor having a cross section ofVarying thickness with its minimum thickness at one of its perimeters,said turn having a uniform overall thickness throughout its entircircumference in a direction parallel to the axis thereof, saidconductor having a circumferential slot therein extending radiallytherethrough' substantially midway between the ends of said turn and ina plane normal to that of the axis of said turn, and said conductor alsohaving a pair of circumferentially separated, longitudinal slots thereinextending through said conductor from the outer to the inner perimeterof said turn and each communicating with said circumferential slot, oneof said longitudinal slots extending from one end of said turn towardsaid circumferential slot and the other of said longitudinal slotsextending from the other end of said turn toward said circumferentialslot to thereby provide a pair of opposed, overlapping terminals spacedfrom each other by said circumferential slot.

8. In electrical heating apparatus, the combination of an inductorcoupling coil comprising a single turn, annular conductor havingoverlapped terminal portions spaced from each other in a directionparallel to the axis of said turn to provide a gap therebetween, and asubstantially single turn, helical supporting member therefor havingoverlapping portions also spaced from each other to provide a second gaptherebetween, said coil having a substantially uniform overall thicknessin a direction parallel to its axis and being secured to said member inconcentric relation thereto, and said gaps being in substantialalignment with each other.

9. The invention set forth in claim 8 characterized by the addition of amember of insulating material in said gaps.

10. The invention set forth in claim 8 characterized in that saidcoupling coil is nested within said supporting member.

11. The invention set forth in claim 8 characterized in that saidsupporting member is of tu-- bular construction and is adapted to have acooling fluid passed therethrough.

12. The invention set forth in claim 8 characterized in that saidcoupling coil has substantially uniform overall thickness throughout theentire circumference thereof.

WESLEY M. ROBERDS.

